Multi-part Gompertz growth problem

Growth of an individual chicken is modelled by the Gompertz differential equation $\displaystyle W'(t) = \mu_0 e^{-Dt}W$. This gives the chicken's weight $\displaystyle W$ (in kilograms) in terms of constants $\displaystyle \mu_0$ and $\displaystyle D$. Time $\displaystyle t \ge 0$ is days after reaching a weight of 0.25 kilograms.

i. What aspect of the chicken growth does the term $\displaystyle e^{-Dt}$ describe?

**I have no idea what aspect this describes. Can anyone point me in the right direction about how to think about this sort of problem?**

ii. Use separation of variables to find the general solution to this differential equation.

**I think I can attempt this one. I'll give it a go and post my working. Essentially I'm finding an equation for $\displaystyle W(t)$ though right?**

iii. In the case that $\displaystyle \mu = 0.068$ and $\displaystyle D = 0.022$, find the time at which the chicken weighs 4 kilograms. What meanings and units do these constants have?

**Is this simply a matter of calculating t using the equation from ii and substituting in the specified variables?**

iv. Does the chicken have a maximum (or asymptotic) weight, and what is it?

**Think I can work this one out once I have ii and iii.**

v. At what time does the value of $\displaystyle W'(t)$ have a maximum? This gives the maximum growth rate of the chicken.

**Think I can work this one out too. Will post working.**